Rheumatoid arthritis (RA) is a chronic and genetically complex inflammatory disorder that leads to erosive destruction of peripheral joints. The use of animal models mimicking RA, such as pristane-induced arthritis (PIA) in rats, should facilitate its genetic analysis. Pristane is a non-immunogenic synthetic oil that, after a single subcutaneous injection into DA rats, induces arthritis restricted to peripheral joints with a chronic relapsing disease course. To identify genes involved in the control of chronic arthritis, we made crosses between susceptible DA rats and resistant E3 rats and analysed the progeny with microsatellite markers covering the entire rat genome. Our results show that different arthritis phenotypes are associated with different chromosomal loci. Loci on chromosomes 4 and 6 (Pia2 and Pia3) influence arthritis onset, whereas a locus on chromosome 12 (Pia4) is associated with severity and joint erosion. We found that chronicity is associated with a different set of loci, one on chromosome 4 and the other on chromosome 14 (Pia5, Pia6). These findings demonstrate for the first time that different phases of a chronic self-perpetuative disease which mimics RA are associated with distinct sets of genes.

Although infection with Mycobacterium tuberculosis (M.tb) induces a robust CD8 T cell response, the role of CD8 T cells in the defense against M.tb, and the mechanisms behind the induction of CD8 T cells, is still not clear. TB10.4 is a recently described Ag that is expressed by both bacillus Calmette-Guérin (BCG) and M.tb. In the present study, we describe a novel CD8 T cell epitope in TB10.4, TB10.43-11. We show that TB10.43-11-specific CD8 T cells are induced at the onset of infection and are present throughout the infection in high numbers. TB10.43-11 CD8 T cells were recruited to the site of infection and expressed CD44, TNF-α, and IFN-γ. In addition, TB10.43-11 CD8 T cells showed an up-regulation of FasL and LAMP-1/2 (CD107A/B), which correlated with a strong in vivo cytolytic activity. The induction of TB10.43-11-specific CD8 T cells was less pronounced following infection with BCG compared to infection with M.tb. By using a rBCG expressing the genetic region of difference-1 (RD1), we show that the presence of a functional RD1 region increases the induction of TB10.43-11-specific CD8 T cells as well as the bacterial virulence. Finally, as an M.tb variant lacking the genetic region RD1 also induced a significant amount of TB10.43-11-specific CD8 T cells, and exhibited increased virulence compared with BCG, our data suggest that virulence in itself is also involved in generating a robust CD8 T cell response against mycobacterial epitopes, such as TB10.43-11.

The ESAT-6 (early secretory antigenic target) molecule is a very important target for T cell recognition during infection with Mycobacterium tuberculosis. Although ESAT-6 contains numerous potential T cell epitopes, the immune response during infection is often focused toward a few immunodominant epitopes. By immunization with individual overlapping synthetic peptides in cationic liposomes (cationic adjuvant formulation, CAF01) we demonstrate that the ESAT-6 molecule contains several subdominant epitopes that are not recognized in H-2d/b mice either during tuberculosis infection or after immunization with ESAT-6/CAF01. Immunization with a truncated ESAT-6 molecule (Δ15ESAT-6) that lacks the immunodominant ESAT-61–15 epitope refocuses the response to include T cells directed to these subdominant epitopes. After aerosol infection of immunized mice, T cells directed to both dominant (ESAT-6-immunized) and subdominant epitopes (Δ15ESAT-6-immunized) proliferate and are recruited to the lung. The vaccine-promoted response consists mainly of double- (TNF-α and IL-2) or triple-positive (IFN-γ, TNF-α, and IL-2) polyfunctional T cells. This polyfunctional quality of the CD4+ T cell response is maintained unchanged even during the later stages of infection, whereas the naturally occurring infection stimulates a response to the ESAT-61–15 epitope that consist almost exclusively of CD4+ effector T cells. ESAT-6 and Δ15ESAT-6 both give significant protection against aerosol challenge with tuberculosis, but the most efficient protection against pulmonary infection is mediated by the subdominant T cell repertoire primed by Δ15ESAT-6.

SummaryIt is known that protection against tuberculosis is mediated primarily by T helper type 1 (Th1) cells but the influence of the Th1/Th2 balance of a vaccination response on the subsequent protection and pathology during infection has not been studied in detail. We designed a panel of Ag85B-ESAT-6 subunit vaccines based on adjuvants with different Th1/Th2-promoting activities and studied cellular responses, bacterial replication and pathology in the lungs of mice infected with Mycobacterium tuberculosis. All vaccines induced cell-mediated and humoral responses but with markedly different interferon-c : interleukin-5 (IFN-c : IL-5) and immunoglobulin G1 (IgG1) : IgG2 ratios. The vaccines promoted different levels of control of bacterial replication with the most efficient protection being exerted by cationic liposomes containing monophosphoryl lipid A and low to completely absent immunity with conventional aluminium. The level of protection correlated with the amount of IFN-c produced in response to the vaccine whereas there was no inverse correlation with the level of IL-5. Characterizing a protective response was an accelerated recruitment of IL-17 and IFN-c-producing lymphocytes resulting in the early formation of granulomas containing clustered inducible nitric oxide synthase-activated macrophages. In comparison, non-protected mice exhibited a different inflammatory infiltrate rich in neutrophil granulocytes. This study indicates that the adjuvant component of a tuberculosis vaccine may be crucial in determining the kinetics by which effective granulomas, pivotal in controlling bacterial growth, are formed.

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